The invention relates to "back planes" and "mother boards" into which a plurality of individual printed circuit boards can be plugged, and more particularly to an improved cylindrical back plane structure for receiving printed circuit boards in generally radial relationship thereto. Most complex state-of-the-art electronic equipment is manufactured by mounting individual components on printed circuit boards. The components are interconnected to accomplish various desired functions, and also are appropriately connected to edge connectors by means of which the individual printed circuit boards can be plugged into mating connectors of "back planes" or "mother boards". Those skilled in the art know that it is common to partition various subfunctions of an electronic system onto various individual printed circuit boards. For example, the memory of a personal computer can be expanded by plugging in additional "memory boards" into additional "slots" that have been made available in the back plane. Although the technique of plugging a plurality of spaced PC boards, each in parallel relationship to the others, and each perpendicular to the back plane, is widely used, there are some problems with this approach. One problem is that a substantial amount of force must be exerted upon a particular printed circuit board in order to plug it into a suitable connector of the back plane. The back plane, which itself is actually simply a rigidly mounted printed circuit board, is inevitably flexed when a printed circuit board is plugged into or removed therefrom. Such flexing can produce hairline cracks in the conductors of the back plane, breaking electrical connections or causing unreliable intermittent open circuits. Adequate cooling of the structure, including the back plane and all of the printed circuit boards plugged therein, presents problems. A major problem of the conventional structure described above is that, since the individual printed circuit boards must be spaced far enough apart to allow efficient cooling, or to allow clearance for tall components to be mounted thereon, signal conductors that are common to different plugged in printed circuit boards must be quite long and have larger amounts of capacitance and inductance associated therewith than is desirable for high speed circuitry. For example, in common conductors that carry high current, the voltage drops across the relatively high resistance, and/or high inductance of the long conductors can cause problems. For example, troublesome "ground loops" may occur as a result of such voltage drops. Such high resistance and/or high inductance can produce undesirably high voltage drops as a result of low currents, if sensitive receiving circuitry is connected to such conductors.
Radial designs for connecting electronic components to a central bussing scheme have been proposed, as indicated in U.S. Pat. Nos. 3,272,933 and 3,265,936. However, the art has not provided a practical, inexpensive cylindrical or radial back plane structure that could be utilized to replace the above-described conventional planar back plane devices.
Thus, there is an unmet need for an improved, economical, easily cooled rigid back plane structure that allows use of the shortest possible common conductors for conducting signals between different plugged-in or bonded in or soldered in printed circuit boards.